Class 12 Biology Chapter 15 Question Answers

Point to Remember for 12 Biology Chapter 15

Reasons for greater biological diversity in tropics

Tropical latitudes have remained relatively undisturbed for millions of years and thus had a long evolutionary time for species diversification.

Tropical environments are less seasonal, relatively more constant and predictable which promote niche specialisation and lead to greater species diversity.

There is more solar energy available in the tropics, which contributes to higher productivity and indirectly leads to greater biological diversity.

Three inter-related levels of Biodiversity

Genetic diversity: Diversity in the number and types of genes, as well as chromosomes present in different species and the variations in the genes and their alleles in the same species. It helps in speciation.

Species diversity: Varieties in the number and richness of the species of a region.

Ecological diversity: Variety in the types of ecosystems.

The importance of species diversity to the ecosystem

Ecosystems with higher bio diversity are more productive than ecosystems with lower biodiversity. David Tilman showed in his experiments that increased diversity contributes to higher productivity.

Biodiversity is essential for the stability of an ecosystem. Communities with more species are more stable than those with less species.

Rich biodiversity is also essential to make an ecosystem more functional and survival of the human race on the earth.

Causes of Biodiversity Losses

Habitat loss and fragmentation: This is most important cause of plants and animals extinction. For example: Tropical rain forest being destroyed faster. The Amazonian rain forest is called the lungs of the planet. It is being cut for cultivating soya beans.

Over exploitation: Many species extinctions are due to over exploitation by humans e.g. extinction of Steller’s sea cow, passenger pigeon in last 500 years.

Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligating way also become extinct.